The universe holds millions of galaxies. Our Milky Way Galaxy formed
between some 10 billion and 15 billion years ago. Based on the ages
of meteorites and lunar rocks, planetary scientists know our solar
system is much younger.

It was born 4.6 billion years ago out of an immense cloud of interstellar
dust and gas that collapsed under the weight of its own gravity.
It pancaked into a flat, spinning disk. Clumps of matter collided
and became bigger, like a snowball collecting snowflakes. The objects
grew so big their gravity began to pull in nearby material, forming
the protoplanets that became our planets today.

Earth is about 4.56 billion years old. Back then, however, it wasnt
Earth as we know it, says Jonathan Berg, chair of NIUs Department
of Geology and Environmental Geosciences. Even if the Earth
wasnt completely molten, the outer
part would have been like a magma (molten rock) ocean, Berg
says. The magma would quickly destroy any crust that formed
on Earth, while heavy elements, such as iron and nickel, would sink
to the center.

Michael
Parrish, chair of NIUs Department of Biological Sciences
and a noted paleontologist, was among the scientists who announced
the fossil discovery
of a mouse-size mammal that lived in Madagascar 165 millionyears
ago. The fossil represents the oldest known modern mammal.

After about 100 million years, Earth began to cool and ocean crust formed,
followed by buoyant continental crust. Over history, the continents
would break apart and collide back together, Berg says. Younger
crust tends to grow around older crust. So it makes sense that today geologists
generally tend to find the oldest rocks in the center of continents.

Scientists in the 1950s through the 1970s analyzed rocks determined to
be more than 3 billion years old. They thought the early Earths
magma oceans and high heat would have consumed and destroyed anything
much older. In the past decade,
geologists, using more sophisticated dating methods that employ high resolution
mass spectrometry, have analyzed layers of grains of zircon in Australias
ancient sedimentary rocks that date to 4.4 billion years.

Zircon is one of the most phenomenal minerals on earth because
its fantastic at surviving and is loaded with radioactive elements,
which allow for precise dating, Berg says. With new mass spectrometry
instrumentation, we can see there were zircons that showed evidence of
having gone through several lives, having crystallized, partially melted
and crystallized repeatedly.

Measurements of oxygen isotopes in zircon also suggest there might have
been water on Earth more than 4 billion years ago. If water was
around, its possible life could have started on earth very, very
early, Berg says. Thats total speculation at this point,
but there could have been early life forms that were repeatedly destroyed.